Amplifier energizing circuit



y 29, 1 H. T. J. WIE GERINCK arm. 1 AMPLIFIER ENERGIZING CIRCUIT FiledJuly 25, 1939 AEAMPL/F/ER HENDR/KUS 7.'J. W/EGER/NCK INVENTORS D T V055EN WW ATTORNEY.-

70 SOURCE OF A 00/0 SIGNALS T0 4.6. RECTIFIER Patented July 29, 1941ABIPLIFIER ENERGIZING CIRCUIT Hendrikus T. J. Wiegerinck and Arnold TheoVossen, Eindhoven, Netherlands, assignors, by mesne assignments, toRadio Corporation of America, New York, N. Y., a corporationof DelawareApplication July 25, 1939, Serial No. 286,320 In Germany March 15, 19393 Claims.-

This invention relates to a low frequency amplifying circuit arrangementcomprising an amplifying tube whose anode circuit contains the primarywinding of an output transformer, the anode voltage produced by apulsating direct current voltage being supplied to the amplifying tubethrough this winding.

It is well known that for simplifying and cheapening the filter circuitwhich is required to smooth the operating currents it is advantageous tosupply to the anode of an output amplifying tube a non-smoothed andconsequently pulsating direct current voltage. Consequently the directcurrent charge of the filter circuit is materially decreased so thatcomparatively small smoothing chokes, or even exclusively ohmicresistances, can be used in the filter circuit. In order to avoid,however, that in this case alternating current voltages originating fromthe pulsating direct supply voltage are produced in the output circuitof the amplifier, which alternating voltages would manifest themselvesas alternating current hum, it is necessary to use means forcompensating the interfering alternating current voltage produced in theoutput circuit.

'This can be achieved, as is well known, by supplying to the controlgrid of the output amplifying tube an alternating current voltage whichhas been taken from the source of anode voltage of this tube. However,the compensating circuit arrangements known to this effect essentiallyexhibit the disadvantage that the grid circuit of the output amplifyingtube is influenced by the circuit elements required for compensation,and this generally in such manner that the frequency response curve ofthe amplifier becomes less favorable. An additional drawback of theknown circuit arrangements is that a control of the degree ofampilfication of the amplifier by means of a variation of the magnitudeof one of the circuit elements of the grid circuit of the outputamplifying tube also brings about a variation of the amplitude and/orthe phase of the compensation voltage supplied to the control grid sothat the compensation is disturbed. Finally, the circuit elementsrequired for compensation frequently act not only upon the grid circuitof the output amplifying tube, but also upon preceding amplifyingstages. The latter is the case, for example, if the compensating voltageis taken from a resistance which is included in the common cathodereturn conductor for the various amplifying tubes. Consequently, verydisturbing coupling phenomena may occur particularly in 7 abovementioned disadvantages are obviated. Ac-

cording to the invention, in a low frequency amplifying circuitarrangement comprising an amplifying tube whose anode circuit containsthe primary winding of an output transformer, the anode voltage producedby a pulsating direct current voltage being supplied to the amplifyingtube through the said winding, use is made for compensating theinterfering alternating current voltages, produced in the output circuitof an output transformer, of an additional winding which is fed by thesource of anode voltage of the said amplifying tube.

By a corresponding choice of the amplitude and the phase of the currentflowing through the additional winding, a faultless elimination of theundesirable alternating currents produced in the output circuit isachieved. It should thereby be noted that the undesirable alternatingvoltages generally contain not only a component corresponding to themains frequency, but also components corresponding to various higherharmonics of the mains frequency.

One particular advantage of the circuit arrangement according to theinvention further consists in that a variation of the degree ofamplification of the relative amplifying tube, as can be produced forexample by means of an eccentric position of the working point of thetube, afiects the compensation of the undesirable alternating currentvoltages to a materially less extent than when the compensating voltageis supplied to the control grid of the tube as in the known circuitarrangements.

To obtain the phase, which is required for compensation, of the currentflowing through the additional winding of the output transformer, theadditional wiring is preferably connected in series with such animpedance that the series connection exhibits a substantially ohmicalternating current resistance.

According to one advantageous construction of the circuit arrangementaccording to the invention, the additional winding of the outputtransformer, which is preferably connected in series with an ohmicresistance, forms part of a filter circuit which serves to smooth adirect current which has been taken from the source of anode voltage ofthe said amplifying tube, said direct current being supplied to the gridelectrodes'of the amplifying tube and, if desired, being further usedfor supplying pre-amplifying tubes.

The invention will be more clearly understood by reference to theaccompanying drawing showing, by way of example, the circuit arrangementof a pentode output amplifying stage according to the invention.

In the drawing, 1 is a pentode amplifying tube, in the anode circuit ofwhich is arranged an output transformer 2. The anode voltage is suppliedto the amplifying tube through a primary winding 3 of the outputtransformer. The loudspeaker 5 is connected to a secondary winding 4 ofthe output transformer. The low frequency oscillations which are to beamplified are supplied to the control grid of the amplifying tubethrough input terminals 6 of the control grid circuit. The directcurrent operating voltages of the amplifier are taken from an existingdirect current mains or a rectifying circuit arrangement, and aresupplied to connecting terminals 1. A condenser 8 is connected inparallel to smooth the pulsating direct current supplied to theterminals 1.

The anode voltage of the amplifying tube I is directly taken from thecondenser 8 so that the direct current voltage set up at the anode ofthe amplifying tube is a pulsating one. This pulsating direct currentvoltage brings about in the secondary circuit of the output transformer2 interfering alternating current voltages which become manifest asalternating current hum. To eliminate the alternating current voltagesbrought about in the'output circuit by the pulsating anode supplyvoltage, the output transformer comprises an additional winding '9 whichistraversed by a current taken from the condenser 8. An ohmic resistance10 and a condenser II are connected in series with the additionalwinding. By a corresponding choice of the ratio between the magnitude ofthe alternating current resistance of the additional winding '9 and themagnitude of the total alternating current resistance of the resistance1 and the condenser I l,the niagrlitude of the alternating voltagebrought about in the secondary circuit of the additional winding 9 canbe adjusted. This magnitude, of course, can also be varied by variationof the number of turns of the additional Winding 9;

If the loudspeaker has a substantially ohmic alternating currentresistance, as is generally the case, the part of the anode circuitwhich is connected in parallel to the condenser 8 has also asubstantially ohmic alternating current resistance, and the circuit ofthe winding '9 which is connected inparallel to the condenser 8 musthave a substantially ohmic alternating current resistance in order thatthe phase of the current flowing through the additional winding 9 iscorrect with respect to the compensation. To this effect, it isnecessary that the additional winding 9 should be connected in serieswith a corre spondingly chosen impedance. Consequently, to compensatevarious interfering frequencies, in the represented circuit arrangement,the ohmic resistance in this case must have a high value with respect tothe sum of the alternating current resistances of the additional winding9 and the condenser ll.

In the represented circuit arrangement the additional winding 9, theresistance l0 and the condenser H constitute parts of a filter circuitwhich serves to smooth the direct current taken from the condenser 8.The direct current voltage set up at the terminals of the condenser H issupplied to the screen grid electrode of the amplifying tube I, and canmoreover be used for supplying further tubes present in the circuitarrangement by taking this direct current voltage from connectingterminals l2.

The condensers 8 and l l serving to smooth the operating currents of theamplifier preferably exhibit a comparatively great capacity, for example32 microfarads. In this case a smoothing, which is suflicient for thepre-amplifying stages, of the direct current voltage set up across thecondenser II will generally be achieved, if the resistance [0 has amagnitude of, say, 2000 ohms.

What is claimed is:

1. In an amplifier, a tube provided with at least a cathode, an inputelectrode and an output electrode, a source of pulsating unidirectionalvoltage, an input circuit connected to said input electrode and cathode,an output transformer having its primary windingconnected between saidoutput electrode and said source, an output circuit connected to thetransformer secondary winding, and means coupled between said source andsaid secondary winding for introducing into the latter a pulsatingvoltage component which cancels out the pulsations due to said source, ascreen electrode adjacent said output electrode, said means functioningas a filter element in said source, and said screen electrode beingconnected to said filter means.

2. In combination with an amplifier tube having signal input and outputcircuits, a source of pulsating direct current voltage, said outputcircuit comprising a transformer provided with a primary winding and atleast two secondary windings, said primary winding being connected to apoint of positive potential of said source, and one of said secondarywindings being included in said source thereby to introduce compensationpulsation voltage into said other secondary winding and a filter networkincluded in said source for smoothing said direct voltage, and said onewinding being included as an element of the filter network.

3. In combination with anamplifier tube having signal input and outputcircuits, a source of pulsating direct current voltage, said outputcircuit comprising a transformer provided with a primary winding and atleast two secondary windings, said primary winding being connected to apoint of positive potential of said source, and one of said secondarywindings being included in said source thereby to introduce compensationpulsation voltage into said other secondary winding and a filter networkincluded in said source for smoothing said direct voltage, and said onewinding being included as an element of the filter network, a screengrid in said tube, and a connection from the screen grid to the outputof the filter network.

HENDRI-KUS T. J. WIEGERINCK. ARNOLD THEO VOSSEN.

